With the development of detection technology, spectroscopy techniques gradually attract wide attention from domestic and foreign scholars due to their fast and easy operations. Terahertz spectroscopy, as a new spectroscopic technique, gradually attracts people's attention. Some vibrational and rotational energy of macromolecules fall in terahertz bands; so terahertz wave is considered to be a very promising method of biological sample detection. For some fields of terahertz spectroscopy techniques with large prospects, such as security, biology, medicine, agriculture and materials characterization, etc., trace amounts of ultrafine NDT is in need in those fields. However, due to disadvantages including low energy terahertz source and limited direct detection sensitivity, it is difficult for terahertz technology to be used in rapid detection of trace amount samples.